Preheat the oven to 350F. Lightly grease an 8-inch cake pan with cooking spray.
In a large mixing bowl, whisk together the dry ingredients. Add the sliced apple and stir briefly to combine.
In a separate bowl, whisk together the eggs, vanilla, oil and yogurt until smooth.
Add the wet ingredients to dry ingredients and gently mix with a rubber spatula until combined. Pour the batter into the prepared cake pan.
Make the cinnamon topping by combining the cinnamon, sugar and butter. Mix together until lumpy and wet. Sprinkle the mixture evenly over the top of the cake batter.
Bake cake for 30-35 minutes, until golden brown and a toothpick inserted into the middle comes out clean. Let the cake cool in the pan for 10-15 minutes, then transfer it to a wire rack to cool completely.
Once the cake is fully cool, make the glaze. In a small bowl, mix together the powdered sugar and 1 tablespoon of milk. Stir until smooth. If the glaze is too thick, add an extra tablespoon of milk. Drizzle the glaze over the cake. Slice and enjoy!